Head-up displays (HUDs) have long been used in airplanes to aid the pilots. The HUD reflects information the pilot needs off of a half mirror or the windshield and projects that information at a distance in front of the plane so that the pilot does not have to look into the cockpit to see the information.
More recently, HUDs have been used in automotive applications in which the image is projected up and reflected off of the vehicle front windshield to appear at a distance in front of the driver. In such cases the front windshield is used as a combiner, allowing the HUD image to appear together with the view through the front windshield. With a HUD in a vehicle, the driver does not have to adjust his/her eyes from the road to read information, such as vehicle speed, which is normally displayed in the vehicle instrument panel.
One limitation of HUDs is the space required for the display source and optics. In the past, the display source and optics of the HUD have been placed in or on the instrument panel. The difficulty in this placement of the display source and optics is that the instrument panel usually has very little space available for such systems.
Another limitation with HUDs reflected off of the front windshield is that the windshield, because of its shape, is an imperfect combiner. The result is that the reflected image often appears distorted. In addition, the image reflected off of the front windshield is not very bright because normal windshield glass does not reflect a high percentage of light.
A further limitation of previous HUDs is that they must be tailored to the specific vehicle model in which they are used, making new model implementation difficult and expensive.
What is desired is a head-up display that does not compete for valuable space in the instrument panel and that provides a bright image of vehicle information so that the vehicle driver does not have to adjust eye focus to view the image. It is additionally desirable to have a HUD that is easily adaptable to different model vehicles.